1. Field of the Invention
The present invention relates generally to electroacoustic transducers and more particularly to an electroacoustic transducer such as an earphone or the like which is worn over or inserted into an auditory opening.
2. Description of the Prior Art
U.S. Pat. No. 4,736,435 discloses a so-called inner-ear type earphone which is inserted into an auditory opening. FIG. 1 shows an example of such an inner-ear type earphone.
Referring to FIG. 1, it will be seen that a driver unit 15 is accommodated within a housing 16. The driver unit 15 is an electroacoustic transducer element and is formed of a diaphragm, a magnetic circuit or the like, though not shown. An external connection cord 17 is extended from the driver unit 15 and is supported by a cord supporting member 18. The cord supporting member 18 is elongated from the housing 16.
As shown in FIG. 2, the housing 16 is made by molding a synthetic resin and is formed in such a size that it can be inserted into a cavum concha b which is a concave portion of an auricle a. When the housing 16 is inserted into the cavum concha b, at least two points of the outer peripheral surface of the housing 16 are supported by a tragus c and an antitragus d which form a part of the auricle a.
The rear peripheral portion of the housing 16, which is opposed to the outside of the auricle a when the housing 16 is inserted into the cavum concha b, is formed as a tapered, inclined portion 19. The inclination angle of the inclined portion 19 is selected so that the inclined portion 19 substantially corresponds to the curved, rising surface of the cavum concha b.
The cord supporting member 18 extended from the housing 16 is downwardly elongated from the lower end of a rear side edge wall 20 of the housing 16 and is substantially parallel to the rear side edge wall 20. When the housing 16 is inserted into the cavum concha b, the cord supporting member 18 comes in contact with a point P3 on the outer surface of a lobe e at the position lower than points P1 and P2 of the tops of the tragus c and the antitragus d. The points P1 and P2 are the supporting points to support the housing 16.
A ring 21 is made of flexible and resilient material and is engaged with a connection portion in which the driver unit 15 and the housing 16 are connected. Referring back to FIG. 1, it will be seen that a protecting plate 22 is located at the front wall of the diaphragm of the driver unit 15. The protecting plate 22 is made of a material such as a metal net or the like having high sound transmission coefficient.
According to the inner-ear type earphone thus made, as shown in FIG. 1, the housing 16 is inserted into the cavum concha b in a three-point supporting fashion so that it can be positively held at one portion of the auricle a without pressing the auditory opening.
In order that any user may wear the inner-ear type earphone shown in the example of FIG. 1 regardless of the size of the ear, in particular, the size of the cavum concha b, this earphone is made in size so as to be inserted into the smallest ear of man.
Accordingly, the thus made earphone is too small for the cavum concha of the larger ear. Thus, when the earphone is inserted into the auditory opening of a large ear, its closed property is poor and the low band sound is lowered and hence a good acoustic characteristic is not expected.